A destroyer may gain more from an AEW drone than a fighter drone

Would fighter drones be the best way to extend a destroyer's defensive reach?

Probably not. An uncrewed rotary or airborne-early-warning asset could extend the sensor horizon and let ship-launched missiles do the fighting.

A useful fighter drone still needs range, weapons, fuel, control teams, maintenance personnel, and a launch-and-recovery arrangement compatible with the ship. The specific 5,000-pound example discussed is neither small nor vertical-takeoff, and a notional group of twenty-four would create a large embarked aviation organization. A sensor drone can deliver the more important marginal benefit - seeing low targets farther away - at lower shipboard cost.